1. Field of the Invention
The present invention relates generally to an apparatus for continuously manufacturing a corrugated sheet. The present invention relates more particularly to the apparatus for the continuous manufacture of the corrugated sheet of a kind that can be used as material for a sleeping pad, a bulky filler material for construction use, cushioning material, a buffering material, material for a gym mattress, a filtering material, and so on.
2. Description of the Prior Art
The Japanese Patent Publication No. 58-19458, published in 1983, discloses an apparatus for manufacturing a corrugated sheet, which comprises an upper and a lower rotary roller having a nipping region defined therebetween, a first conveyor means including first upper and lower conveyor belts and positioned downstream of the nipping region with respect to the direction of feed of a web of sheet to be corrugated, and a second conveyor means including second upper and lower conveyor belts positioned on one side of the first conveyor means remote from the nipping region. The second conveyor means is driven at a speed lower than that of the first conveyor means so that the corrugated sheet having a fold width generally equal to the spacing between the upper and lower conveyor belts of any one of the first and second conveyor means can be manufactured.
The Japanese Laid-open Patent Publication No. 3-49928, published in 1991, discloses a similar apparatus which comprises a pair of toothed wheels for imparting fold lines successively on a web of sheet during the passage of the web of sheet through a gap between the toothed wheels, upper and lower pressing rollers having a gap defined therein for the passage of the web of sheet, which has been imparted with the fold lines, thereby to bend the web of sheet in a generally zig-zag fashion along the fold lines, and upper and lower shaping rollers for imparting wrinkles to the corrugated sheet. In this prior art corrugating apparatus, the speed at which the corrugated sheet is transported through the gap defined between the upper and lower shaping rollers is chosen to be lower than that at which the web of sheet is transported through the gap between the upper and lower pressing rollers, so that the corrugated sheet having a fold width generally equal to the height of each tooth of any one of the upper and lower toothed wheels can be formed.
According to the first mentioned publication, the choice of the difference in speed of transport between the first and second conveyor means and also that of the spacing between the upper and lower conveyor belts of any one of the first and second conveyor means are essential to manufacture the corrugated sheet having a predetermined fold width. Where the fold width is desired to be changed, the difference in speed of transport between the first and second conveyor means and that of the spacing between the upper and lower conveyor belts of any one of the first and second conveyor means have to be altered.
The prior art corrugating apparatus according to the first mentioned publication has a problem in that, since each of the upper and lower conveyor belts of any one of the first and second conveyor means are supported only at its opposite ends, at least respective runs of the upper and lower conveyor belts which confront with each other tends to be slackened, resulting in the formation of the corrugating sheet having an irregular fold width.
On the other hand, according to the corrugating apparatus disclosed in the second mentioned publication, since the tooth grooves in one of the toothed wheels and the tooth tips in the other of the toothed wheels cooperate with each other to define the fold width possessed by the eventually corrugated sheet, it is possible to manufacture the corrugated sheet having a uniform fold width.
However, the prior art corrugating apparatus disclosed in the second mentioned publication has a problem in that, since the fold width of the eventually corrugated sheet is necessarily determined by the interaction between the tooth grooves in one of the toothed wheels and the tooth tips in the other of the toothed wheels, a replacement of the toothed wheels of one particular size with those of a different size is required if the corrugated sheet having a different fold width is desired to be manufactured. This replacement is indeed complicated and time-consuming because the once-installed toothed wheels of one particular size have to be removed from the machine framework, followed by a mounting of the toothed wheels of a different size.
Also, none of the above mentioned two publications disclose means for manufacturing the corrugated sheet having the fold lines which extend in a zig-zag fashion over the width thereof.
In view of the foregoing problems found in the prior art corrugating apparatuses, the inventors of the present invention have carried out an extensive development of an improved corrugating apparatus substantially free from the foregoing problems.